With the development of integrated circuits toward high density and high performance, the reduction of line width requires a light source with the reduced wavelength. Under said circumstances, the planarity of the wafer surface and the cleanness of a wet process are both relevant to the manufacturing yield. If the chemical mechanical polishing technique is applied for planarization, the polishing agent used in the technique is the factor of the polishing quality, and thus the quality control lies in the management of the size distribution of the particles in the polishing agent. In addition, particles and impurities in the solutions (e.g., hydrogen peroxide, a photoresist cleansing solution, ammonia, a developer, and so on) applied in various wet processes also pose an impact on the manufacturing yield and thus call for the attention from semiconductor manufacturers. In order to control quality through 24-hour online monitoring of the size distribution of the particles in a solution, a 24-hour automatic sampling and mixing apparatus has been developed. Given the fixed dilution rate and the even mixture, the relative concentration of the monitored solution can serve as the basis of quality control.
In general, the polishing agent may be mixed with a dilution agent for adjusting its concentration. However, the particles in the mechanically stirred polishing agent may aggregate or fall off, and therefore the use of mechanical mixing equipment (e.g., a stirring magnet or a cyclic pump) for stirring the solution may be prohibited. The mixing effects achieved by a non-mechanical static mixer are proportional to the effective mixing length; the greater the length of the static mixer, the better the mixing effects achieved. The increase in the length of the mixing equipment, however, also leads to the increase in the space occupied, and therefore it is rather unfavorable to integrate multiple non-mechanical mixing equipments into a miniaturized machine.
At present, the common tools for particle size inspection include a particle size analyzer and a liquid particle counter which are capable of monitoring the size distribution of particles in a liquid solution or monitoring the number of particles in the solution, and the minimum detectable size of the particles may reach 40 nm-200 nm. The widely-applied line width in the existing semiconductor manufacturing process is at most 28 nm, and thus neither the resolution of the particle size analyzer nor the resolution of the liquid particle counter can satisfy the industrial requirement for online monitoring of the nano-scale particles in the solution.